Merge pull request #1142 from DougGregor/throwing-macro-expansion

Author: DougGregor

Sources/_SwiftSyntaxMacros/ExpressionMacro.swift

@@ -21,5 +21,5 @@ public protocol ExpressionMacro: Macro {
   static func expansion(
     of node: MacroExpansionExprSyntax,
     in context: inout MacroExpansionContext
-  ) -> ExprSyntax
+  ) throws -> ExprSyntax
 }

Sources/_SwiftSyntaxMacros/Syntax+MacroEvaluation.swift

@@ -13,23 +13,18 @@
 import SwiftDiagnostics
 import SwiftSyntax
 
-extension MacroExpansionExprSyntax {
-  private func disconnectedCopy() -> MacroExpansionExprSyntax {
-    MacroExpansionExprSyntax(
-      unexpectedBeforePoundToken, poundToken: poundToken,
-      unexpectedBetweenPoundTokenAndMacro, macro: macro,
-      genericArguments: genericArguments,
-      unexpectedBetweenGenericArgumentsAndLeftParen, leftParen: leftParen,
-      unexpectedBetweenLeftParenAndArgumentList, argumentList: argumentList,
-      unexpectedBetweenArgumentListAndRightParen, rightParen: rightParen,
-      unexpectedBetweenRightParenAndTrailingClosure,
-      trailingClosure: trailingClosure,
-      unexpectedBetweenTrailingClosureAndAdditionalTrailingClosures,
-      additionalTrailingClosures: additionalTrailingClosures,
-      unexpectedAfterAdditionalTrailingClosures
-    )
+/// Diagnostic message used for thrown errors.
+struct ThrownErrorDiagnostic: DiagnosticMessage {
+  let message: String
+
+  var severity: DiagnosticSeverity { .error }
+
+  var diagnosticID: MessageID {
+    .init(domain: "SwiftSyntaxMacros", id: "ThrownErrorDiagnostic")
   }
+}
 
+extension MacroExpansionExprSyntax {
   /// Evaluate the given macro for this syntax node, producing the expanded
   /// result and (possibly) some diagnostics.
   func evaluateMacro(
@@ -41,7 +36,19 @@ extension MacroExpansionExprSyntax {
     }
 
     // Handle the rewrite.
-    return exprMacro.expansion(of: disconnectedCopy(), in: &context)
+    do {
+      return try exprMacro.expansion(of: detach(), in: &context)
+    } catch {
+      // Record the error
+      context.diagnose(
+        Diagnostic(
+          node: Syntax(self),
+          message: ThrownErrorDiagnostic(message: String(describing: error))
+        )
+      )
+
+      return ExprSyntax(self)
+    }
   }
 }